Application of a new theory of restraint factor after cracking of reinforced concrete members

A detailed tie model of cracking is proposed. The model is dedicated to both semi-massive RC (reinforcement concrete) members subjected to early-age imposed strains and non-massive members in which imposed strains occur after concrete hardening. As distinct from the currently applied European guidelines, the proposed model enables an analysis of crack width changes. These are a function of progressive imposed strain, material and geometry data, but also depend on the scale of cracking which determines the strain conditions of a member. Consequently, the new model takes account of not only the factors determining the cracking development but also the member relaxation effect that results from cracking. For this reason a new definition of restraint factor is proposed, which takes into account the range of cracking of a structural member, i.e. the number and width of cracks. Parametric analyses were performed of both the changes of the degree of restraint after cracking as well as the changes of crack width depending on the adopted type of aggregate, class of concrete and the coefficient of thermal expansion of concrete. These analyses indicate the potential benefits of the application of the presented model for both a more accurate interpretation of research and economical design of engineering structures.